It is often desirable to communicate information digitally. In particular, voice and/or data information carried over various communication networks are often transmitted digitally. For example, in North America standards have been established for a digital hierarchy to transmit digital bit streams in various multiplexing levels. These digital signals are referred to as DS-n, wherein n refers to the multiplexing level of the digital signal stream.
In order to provide control and maintenance functions associated with the digital transmission of data, the digital data streams are divided into overhead and payload. Overhead functions include framing, error checking, and maintenance. Payload capacity is used to carry signals delivered from the next lower level or delivered directly to the multiplexer by a subscriber.
The transmission of digital data streams may be synchronous or asynchronous. The transmission of bit streams according to the DS-n standards is asynchronous. Whereas, synchronous optical network (SONET) is a synchronous transmission vehicle that is capable of synchronous transmission of payloads in the gigabit range. In order to transmit asynchronous data packets, such as the aforementioned DS-n data streams, standards have been established to carry asynchronous data streams in a synchronous bundle, such as those of SONET.
However, as the asynchronous data packets transported by the synchronous bundles may have a velocity both with respect to the synchronous bundle and themselves, i.e., the asynchronously supplied data may drift in its relative placement within the synchronous transport container, the use of various overhead bytes, such as pointers, are used. For example SONET utilizes a pointer which indicates the alignment of the payload within the SONET bundle. Moreover, as the asynchronous payload is allowed to drift within the synchronous transport container, often the only bits/bytes that are placed within the transport container bundle at a fixed position are ones of the above described overhead bits/bytes, such as the pointer bits/bytes, thus adding complexity to any downstream operation with respect to the payload. Yet further complexity is introduced in order to accommodate variation in the rate input of the asynchronous bit stream, as use is often made of positive stuff bits/bytes to accommodate slower than nominal bit rates and/or negative stuff bits/bytes to accommodate faster than nominal bit rates.
In order to transmit a large amount of information and the associated overhead bits/bytes, a substantial amount of bandwidth is required. For example, the above described SONET communication standard is capable of transmission in the gigabit range. However, such large bandwidth links are not always available to all subscribers seeking communication over such a network. For example, a subscriber may be located in a building not served by an fiber optic trunk, nor may such service be cost effective. Likewise, a subscriber may be located remotely, substantially isolated, from any urban area having large bandwidth communication infrastructure.
Accordingly, there is a need in the art for providing a link adapted to allow such subscribers to communicate via an established network infrastructure, which is more cost effective and/or easier to deploy. For example, wireless point to point or point to multi-point links may be simply and cost effectively deployed to provide links with existing communication infrastructure and such subscribers not initially served by the infrastructure. However, such secondary links may not be able to provide the same bandwidth or may otherwise require the repackaging of communicated information in order to provide the desired link attributes. For example, the above mentioned wireless links may be bandwidth limited and, therefore, benefit from the use of more efficient data transport containers in order to provide data throughput commensurate with that of the established network infrastructure.
However, as such a link is to provide communication between a remote subscriber system and an established network infrastructure, the link is preferably transparent. Transparency may be achieved through the communication of data packets native to the established network infrastructure. Although the payload might be dropped out of the communication network""s native data packets, i.e., the transport containers demultiplexed, and broken down to their lowest level of raw data, for transmission over such a secondary link and therefore native data packets fully reassembled from this raw data at the receiving end, this requires time, adding latency, as well as requiring substantial processing power and equipment. Accordingly, there is a need in the art to provide the aforementioned link communicating as high of level of native data packet as possible in order to reduce latency and equipment requirements. There is a further need in the art for the transport container used by such a link to accommodate drift in the placement of payload within the native data bundle.
These and other objects, features and technical advantages are achieved by a system and method in which a transport container is utilized to carry relatively high level communication network native data packets from a hub or other equipment coupled to the communication network infrastructure to a remote, or plurality of remote, network nodes. In a preferred embodiment of the present invention the link utilized for transporting the information utilizes a radio frequency (RF) carrier where the data transport container is specifically adapted to allow the transport of more payload/bandwidth.
In a preferred embodiment the transport container is an airlink transport container (ATC) adapted to transport communication network native data packets. For example, where the communication network to which the aforementioned hub is coupled is a SONET network, the network native data packet is preferably a VT1.5 transport container. This is preferred as, especially at the hub portion of the link, there may be a large concentration of traffic, up to 336 VT1.5s each containing a DS-1 at the hub. By transporting the higher level VT1.5 data packets, instead of the lower level DS-1s included therein, dropping 336 DS-1s from their VT1.5 containers, i.e., removing the DS-1s from their VT1.5 transport containers and framing them up, is avoided. This is advantageous as the circuitry to drop this number of DS-1s from their containers is considerable in cost, space, power consumption, etcetera.
Moreover, advantages are realized in transporting the higher level data packets in subscriber end flexibility. For example, the preferred embodiment transporting VTl.5 transport containers within the ATC of the present invention are able to interface with SONET equipment at the subscriber premises thus providing a truly transparent SONET type link. Additionally, or alternatively, only relatively few (in the preferred embodiment 1 to 11) DS-1 s (those actually transported) need be dropped from an RF carrier at the subscriber side for interfacing with DS-1 equipment, thus avoiding dropping all DS-1s from their VT1.5 containers at the hub when only a portion are actually used at the remote site.
In the preferred embodiment the transport container of the present invention is a synchronous transport container that can accommodate multiple asynchronous payloads. These asynchronous payloads need not have a fixed timing relationship to each other or to the transport container of the present invention. Accordingly, the present invention is adapted to accommodate the DS-1 payload envelope floating within its VT1.5 transport container.
The transport container of the present invention, although providing communication of the relatively high level native data packets is adapted to do so with improved bandwidth efficiency through the use of compression of overhead bytes, dropping of redundant information, discarding reserved space, carrying payload in place of repetitive overhead information, utilizing more efficient error correction techniques, and the like. However, the transport container of the preferred embodiment of the present invention is transparent in that, from the perspective of the payload, it is as though the transport container is not in the circuit at all. Accordingly, the preferred embodiment of the transport container does not cause frame slips and does not require slip buffers.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.